Pulse simmer flash lamp cathode

Abstract

A flash light operating in the "pulse and simmer" mode has a cathode and an anode 18 mounted at opposite ends of a transparent envelope 10. The cathode, which may be water cooled, includes a mount 24 and a tip 26 joined to the mount by an undercut neck portion 28. Thus the tip 26 runs at an increased operational temperature due to the reduced thermal conductivity of the neck portion. The ratio of the diameter D of the tip 26 to its axial dimension C from the neck portion 28 may be in the range 0.3 to 0.5.

We claim: 
     
       1. A pulsed flash lamp designed to operate in a pulse and simmer mode comprising: a transparent envelope;   an anode and cathode mounted in said envelope in an axially confronting relationship said cathode comprising mounting means of an electrical and heat conductive material, and an electrically conductive tip;   a cooling means provided for cooling said cathode; and   means for providing a pulsed electrical current to said cathode;   wherein said mounting means includes a neck portion of a reduced cross-section to support the relatively large cathode tip whereby the neck serves to reduce the thermal conductivity of said mounting means to enable the cathode to operate at an increased operational temperature, and wherein said cooling means is thermally coupled to said mounting means;   
     
     
       2. A flash lamp according to claim 1 in which the cathode tip directed is generally of a mushroom shape having a diameter greater than its axial dimension from said neck portion. 
     
     
       3. A flash lamp according to claim 1 in which said thermal conductivity is reduced by increasing the length of said neck portion. 
     
     
       4. A flash lamp according to claim 3 in which the face of the cathode tip directed towards said anode is generally ellipsoidal and the ratio of its diameter to its axial dimension is within the range 0.3 to 0.5. 
     
     
       5. A flash lamp according to claim 1 in which the cathode tip operates at a temperature in the order of 1,400° C. 
     
     
       6. A flash lamp according to claim 1 in which said cathode tip is made of tungsten, mounting means is made of a thorated tungsten. 
     
     
       7. A pulsed flash lamp designed to operate in a pulse and simmer mode comprising: a transparent envelope;   an anode and cathode mounted in said envelope in an axially confronting relationship;   mounting means for mounting a tip of said cathode and for providing controlled cooling of said tip such that temperature variation of the tip during pulsing is reduced and excessively high temperatures are avoided, said mounting means including a cathode mount and a neck of reduced cross-section, said neck extending from said cathode mount to said tip and providing a reduced thermal conductivity portion of the mounting means to prevent rapid dissipation of heat from said tip through said neck and thereby reducing temperature variation of the tip during pulsing;   cooling means termally coupled to said cathode mount to remove heat from the cathode thereby avoiding excessive heating of said cathode while preventing large temperature variation and large temperature gradients in the tip during pulsing as a result of the reduced thermal conductivity neck extending between the cooled cathode mount and the tip.   
     
     
       8. A method according to claim 7 which the operating temperature of the cathode tip is in the order or 1,400° C. 
     
     
       9. The pulsed flash lamp of claim 7, wherein said cathode mount has a cross-section which is substantially larger than the cross-section of the neck. 
     
     
       10. The pulsed flash lamp of claim 7, wherein the cathode tip is generally of a mushroom shape. 
     
     
       11. The pulsed flash lamp of claim 7, wherein the cathode tip directed towards said anode has a ratio of its diameter to its axial length in the range of 0.3 to 0.5. 
     
     
       12. The pulsed flash lamp of claim 7, wherein the cathode tip includes tungsten, and the mounting means includes thorated tungsten.